DESCRIPTION Normal development of the cerebral cortex, including the formation of appropriate corticothalamic projects is required for higher sensory and cognitive functions. One would predict that interference in the normal development of these pathways could result in, for example, cognitive defects observed in many congenital birth defects affecting the central nervous system. Furthermore, there is increasing evidence that developmental defects may even underlie disorders that are first manifested later in life. These studies focus on defining how the absence or over-expression of hepatocyte growth factor during development affects the subsequent assembly of normal circuits within the forebrain. The ability to generate animals with abnormal corticothalamic circuits will, in the future, provide models to test how modest defects at the molecular level can lead to long-term abnormalities. Furthermore, an understanding of development mechanisms can be used in the re- establishment of connections after injury.